Electrical measuring device



De@ 4, 1934. E. HscHRl-:1BER 1,982,766

ELECTRICAL MEASURING DEVICE Filed Sept. 26, 1933 ATTORN EY V r"Another purpose-of;1,the invention is byfmeansr offarrintegrating device which will Patented Dec. 4, 1934` l `ELEfrrRIoAr. MEASURING nEvIoE l )Ernst-,Hoferchreiber, LosyrAaxgeles, alii,V y

signor` toAmerican Telephone and Telegraph Company, a corporation oAf NeW York Applieationseptember zaiesaseriai No. 691,074: f' aolaims.' (ci. 13e-.mf

f invention frelates l to methods and means for. checking telephone circuit equalization, and more particularly applies .to circuits used for `trai,ismitting by wire' suoli` `as transcontinental 5, lines; programs'.A for broadcasting stationsgor other purposes;

,"lfntha use of vsuch lin-'es itis important to check now again on the transmission characteristics f `thecrcuit or line to see Athatthe transmission level or gain` does'n'ot rise or fall beyondcertain specified .limits,', and more particularly does not alterrelativelywitliin the 'frequency 'spectrum being used. Due to vextreme changes in the equivalents of the, facilities in. usewithchang'es in temperalture rand. humidity t alongja transmission'. line, the frequency characteristics of Ythe t signalY received at thejremoteend `of `a long circuitmay v show bad distortion.' These changes are 'ordi' narily compensated for part by daily tests made oneatfhi of the unitsA making .upthe completev cir-ff cuit. i Howev'en with the., 4deviations necessarily allowedin the liner-up` fof each of the separateY units, it possible the overall circuitlmay h zafvef` considerable variation over the: `:frequency rangegif the deviation sciimulati've.v @Furthermore, in a circuitshavf y an overall gross' equiva-` lent-` ofA several` hundred .clecibels,A the deviations may assume fairly large prOpOrtiOnsWithchang.-

weather conditions. For these reasons, itnay 3o badesirable to take, measurements` and make correspondingadjustments during intervals'lbetween partst'ot the prograrn, using'iconstantV power urces at: one. pointv and suitable measuring, instruments `at` another p oint.` This,n however, is 35 dim'cult for` thev reasonthat. the intervalsy between thediiierent parts ,o apr'ogram are-quite` short,

and the presentlyterirlency,l is-*to Areducethese 'telllflS-4 nl 5;; lThepurpose` oathis invention is to devise.1 a

-`450 method andAV means by which thev transmission equivalent or any sectionfof a: signaling network, orfvany nmnberof sections lined up forfthrough transmission; may be found. withoutremovimalhe section or; sections.from;service;`` l y l todo this tegraitei overafperiodtof sui-table :t length `to permit, upon ready observation at the two stations irrvolved, ani exchange: of' information on a 'useful Still another purpose ofthe invention' is: to deviselsuchk anf integratir'ig` device which will be simple and rugged andr yet' of sufficientl sensitivity. The uinetliod .of the? invention: consists-in the applicatiomofiloand-passi lters to-bothi endsjof the circi'iitor` line under consideration, followed or preceded by Suitable amplifiers. A comparison ofthe respective'powerllevels withina frequency band, utilizing the actual program or other 'signal-1 ingmaterial, is then' to, bjenladeby` means .of an integrating device 1 for indicating the average power` or the totalenergy over a'denite period of time.4 'Simultaneousobservations are to be madetheftvvc)` ends kand the4 information exchanged. The' processkis then repeated for other portionsV oil the 'frequericy,ranger whereupon the necessary circuit adius'tmentscan be made to bring about transmission equalization throughout the `signalingspectrum. In practice' I findthat it is not necessary- 'to "take measurements 'orY observations over the whole signaling 'frequency spectrum or band. 'but in; the. ease, y f o ,example10i4 a Circuit covering. a SQOQcycIeband it would, in general, 'e'satisfactory to `tal/ie"ine'asuremerits onA the' power the bahdSlOUfO 300,180() t0 160035116.' 2500 to 4500. cycles@V j', Y I VfThe invention willfloeA liejtte'r" understood by *NT* "omas reference to the following'gspecication andthe accompanyirig` drawingfin. which Figure 1A is a schematit;` .diagram of :tlieprogram circuit Awith the; devices` necessaryfor this invention; Fig. 2

` showsoiieform of integrating device-constitut ing. apartfof my invention; Figi-3Y shows the char-l -acteristic of` a'de'vicjeof. the shown in Fig.' 2; Vand Fig Lillustrates the type'ofrecord which Referring more specifical'lyjto Fig. H1j, a program'. circuih normally comprising a Vtransmission lineof'a pair of. wires,"is' shownwith two stations at which'ui'tablejequalizers' 10 4and 1l are located, thesepreferablybeing adjustable and being supplemental' to such others as may already be.- inthe line." The twojme'asuring poi-ntsy may beseparated by as' wide 4a: space as desired. Bridg'ed' acrossftlie"Iine-at the poi-nt' 11'2 is an ampli''er' A1, totthe output ofiwhiclrwouldbettachedaplurality of band-pass ltersfconnected preferably in paralleli and adjusted to any con:- venient' frequency bai-rds; Aas arr illustration, for example, these band-pass filters F11, F1 and. F3 migl-i-t` well be adjusted 1to1 the frequency bands mentioned above. AThe outputfof each of these band iltersListheI-i impressed upon suitable power averaging circuits orY integrating devicesA P1', P2 and Per respecti-vely,l the outputof each of these goest to suitable indicating meters Mi, M2 and These integratingdevices with their meterslmayltake on-,al variety of forms, one preferred form being described in greater detail'. be-

low. Inany event their character should be such that they indicate not the instantaneous power, which of course is subject to very sudden and numerous changes, but should be such that they are slow enough in action to permit a signiiicant observation, which may then be transmitted to some other point.

The equipment at the second measuring point may be identical in every respect to that at the first measuring point, and the observers or operators at the respective stations are provided with some suitable independent communication channel, such as a telephone or telegraph line, shown at 15, and which may be spoken of as a coordinating circuit.

Referring now more specifically to Fig. 2, there is shown a device whichY 11i-ind suitable las `an integrating device to be used in the circuit of Fig. 1. In this Fig. 2 there is shown a fiat metal member 21 around one end of which iswound a wire, which I preferably use in the bare form, insulating this bare wire from the metallic plate 21 by suitable insulating strips' 24. Connected to the metal plate 21 is some other metal 26, thetwo together forming a thermojunction, the circuit for this thermojunction comprising the metallic plate 21, the second metal 26 and suitable conductors 27 which lead to an indicating instrument such as a microammeter 28. The coil 22 is associated with one ofthe band filters either directlyy or through the medium of suitable amplifying or other `power controlling devices. The

current passing through this wire winding pro-y duces suicient heat to appreciably raise the temperature yof that portion of the metal strip 21 immediately under the winding.A The shape of the metal plate 21 vand the proximity of the connecting wires to the heating coil are such as to set up a temperature difference between the two junci that a very wide variety of choice *of pairs of metals or alloys is available for the purpose. The portion of the plate 21 which I designate the cooling iin is suiiiciently long so that `the remote end maintains'a substantially constant tempera- K' turel and, in general', is not far ldifferent fromthat of the surrounding air. In order to prevent disturbances-due to air currents I iindit' desirable to place this whole device in some protecting box 29. It is evident that in a device of this character there is a, cor'isiderableI lag between any change of current in the heating coil 22 and the resultant effect in the thermojunction circuit, and this lag is such as to very largely Wipe out the numerous fluctuations and give a reading on the rammeter which is a kind of integrated effect taken over a reasonably long intervalr of time. l The reading constitutes, as it were, a running average of the current in the heating coil in which the effects of the first and last portions are weighted less than the intermediate portion for the reason that the rst portion involved in theintegration has largely lost its effect and the last portion has not yet had full opportunity to make itself felt. The characteristic of one such device is illustrated in Fig. 3, in Vwhich a log-log plot of the power delivered to the heating'lcoil or grid 22. and the vreading of the microammeter are shown.- It will be noted that the characteristic thus plotted is substantially a straight line, and an analysis of this curve will show that it is represented by the equation where p is the power in watts andi is the current in microamperes. l n p I rI'he'behavior of this integrating device in response to a definite program comingover a transmission line is indicated in Fig. 4 in which time minutes is plotted along the horizontal coordinate and the relative power level in decibels is plotted in the vertical direction. The curve a records the readings of the microammeter taken at ve-second intervals for a program of opera music, and curve b is similarly obtained for a program partly vocal and partly speech. It will be observed that the numerous and sharp fluctuations in power level characteristic of such signals have largely disappeared and that the indicator or needle of the microammeter goes througha slow motion. The position of the needle may be observed at any moment, whereupon the'information on this may be sent to the other station for comparison with readings on an identical system. As shown in Fig. 1, observations are to be made substantially simultaneously ony three frequencybands, and the readings of the three instruments at the one end should be related to each other inv the same way as the readings of the instrumentsy at the one station or the other, such as throughV at the other end. If the readings are not'so related then adjustment for equalization is made the adjustable equalizers 10 or 11.

It will be recognized that as a rule the'energy present inthe higher frequency range will be considerably less than for the lower frequencies. For this reason it will usually be desirable to introduce fixed losses or gains, by attenuators or amplifiers, in one or another of the measuring circuits in order to make the readings of the meters vacuum tube integrating device which might in-f' dicate the total energy, starting at any particular time and proceeding for a definite period. Also, it might be any of the standard forms of volume indicators', yalthough these changetheir indications so rapidly as tomake it ldifficult to take a reading of significance andcompare it with the reading at the same moment at the other station. The advantage of the particular device here described is that it does not require accurate timing at the measuring points, and merely requiresa comparison of the readings of two slowly moving indicating meters at any desired time. The slowness of this movement, that is, the interval over which the running average is obtained, can-.ob-

viously be made of any desired value-by changes inthe dimensions and proportions of the device `of Fig. 2. y f

While the invention shows an amplifier bridged across the line at one of the measuring stations, this amplifier in 'turn feeding into band iilte-rs, it should be understood that such ampliersare not necessary, but the band filters may be bridged directly across the line. This, in general, is not a desirable arrangement for theampliers-serve iro iso

a double purpose-first, they give increased power delivery to the band filters, and second, in their usual form they constitute a voltage-operated connection which does not drawan appreciable amount of power from theline or affect its characteristics in a significant Way. l

` The invention has been described particularly with reference to its use for maintaining equalization of loss or gain throughout the signal frequency band between any two points on a, transmission line. But it is evident that upon suitable calibration of the equipment it may -be used for indicating at one point the actual energy level of an incoming signal orany portion of its frequency range. .And it is evident, also, thatvit may be used for other purposes which will be apparent to those skilled in the art.

What is claimed is:

1. In an integrating device for signaling currents, a metal member, a heating coil for carrying the signal currents adjacent to the metal member and unsymmetrically located with respect to it, and a second dii'erent metal element connected to the first near the coil to form a thermojunction circuit.

2. An integrating device for telephonie signal currents comprising a at metal member, a heating coil for carrying the signal current wound around and near one end of said member, and a Wire of a second different metal connected to the rst 'lat member near the coil to form a thermojunction circuit. I

ERNST I-I. SCHREIBER. 

